From the publisher:
Defenders of Shalvion is a semi-cooperative and all-vs-1 game for 3-8 players.
The various factions of the galaxy Shalvion have been fighting amongst themselves for ages. Now, however, a new threat arises, threatening to drive them all to extinction: Miasma. As Defenders of Shalvion, players will take on a role of one of 6 factions, or the villainous Miasma.
Game play begins with a card drafting phase in which most players will draw 7 cards and choose 1. They will pass the remaining cards to the left. Choose 1. And continue down until there is 1 card left. This card is added to the others to create a Miasma Deck. Then the real game begins.
During the Defender Phase, players will choose 1 card to play, with the option to boost their cards with resources. (If the card represents a player's own faction, the card may be boosted without resources.) After this action has been taken, the players will then gather resources from any planets they control, and send their ships to attack the threat.
During the Miasma Phase, 1 card is flipped. Miasma gains resources and takes an action against the players. (Miasma may also be an active player, in which, the player decides which card to play.)
Players will need to watch that Miasma does not gain too many resources and become too powerful. If Miasma survives 5 rounds, Miasma wins. If Miasma gains too many resources or defeats all factions, Miasma wins. But if the factions are able to defeat Miasma, they will gain points according to their faction's unique victory conditions. And the player with the greatest number of points wins the game.